1. Field of the Invention
The present invention relates to a material and apparatus for cleaning critical imaging surfaces in various printer devices.
2. Description of the Related Art
In conventional plain paper copying machines the image is typically formed on a photoconductor, transferred to the paper, and subsequently passed through a thermal fixation roll and a pressure roll. The image is created by toner which is typically a mixture of a thermoplastic and carbon. As the paper passes through the nip, the toner which faces the hot fixation roll melts and flows into the paper. This area of copiers and printers is typically referred to as the "fuser".
The image which is created by the toner is transferred to multiple surfaces. It is important to achieve high levels of transfer of the image from one surface to another. When incomplete transfer occurs, it is necessary to clean any residual toner off of the surface, or the non-transferred toner will be deposited on subsequent pages, thus causing "offset". Offset is any undesirable marks, spots, or smears that may appear on a printed sheet. Any surface that is involved with forming or transferring the image will hereafter be referred to as a "critical image surface". Critical image surfaces include, but are not limited to, photoconductors, other image forming surfaces such as rollers or drums, paper feed rollers or belts which transfer the paper containing the image, intermediate image transfer surfaces such as belts or rollers, and fuser rollers or belts which fix the image to the paper.
The primary imaging surface in conventional printers, typically a photoconductor, is typically an aluminum mandrel coated with one or more photoconductive materials, such as selenium or the like. It is extremely important to keep this surface clean and free of surface defects. It is therefore important to clean the photoconductor surface with a material that is non-abrasive. Abrasion to the photoconductor surface may lead to inadequate image formation, excess ionization of the surface, poor image transfer, and recurring offset.
The fuser rollers typically comprise a heated fixation roller and an elastomeric pressure roller. The trend in the non-impact printing industry is to coat these rollers with a fluoropolymer layer which acts as a release surface and decreases the amount of offsetting. The non-stick fluoropolymer layers are used in conjunction with a release agent, typically silicone oil. In order to prevent the toner from sticking to the fixation roll during fusing of the image, a release agent is typically applied to the fixation roller. Silicone oil, or dimethylsiloxane, is currently the release agent of choice in most copier and printer applications. The release agent is transferred to the paper during fusing. When an insufficent amount of release agent is present on the fixation roller, the toner will become adhered to the fixation roller during the fusing process and can become deposited on subsequent pages, creating offset. With the use of fluoropolymer release layers, the amount of silicone oil needed to prevent offsetting has been dramatically reduced. Moreover, in some printers, no release agent is used.
Other critical surface components within the printer are also currently being coated with release layers. For example, paper transfer belts are commonly spray coated with a release material to promote efficient image transfer. However, with these release coatings some offsetting occurs.
The trend in the non-impact printing industry is to produce images with higher resolution. This means that there are more dots per inch (DPI) on prints and copies. In order to achieve this finer resolution, the toner particle size must be smaller, which has led to some problems in controlling the particles. The small particles are more difficult to transfer from one surface to another, they float about more readily, and thus often result in undesirable coatings on certain surfaces. In addition, the smaller particles are more easily caught or trapped in grooves, pockets or other surface defects of the critical image surface. It is also more difficult to clean these smaller particles off of critical image surfaces. The existing cleaning materials are not only inadequate at cleaning these small particles, but also are abrasive, which leads to increased critical image surface wear.
The trend in the non-impact printing industry is to provide materials and methods of cleaning that are less abrasive to the critical image surfaces, especially the photoconductor. In light of the smaller toner particles, the cleaning material must be extremely conformable to the surface to be cleaned.
Most of the conventional cleaning materials used in this industry are nonwoven mixed fiber webs. For example, initially a high temperature fiber material such as aramid fiber was made into a light nonwoven web using a binder to hold the web together. This material worked well in some applications, but caused a variety of problems in others. The high temperature aramid fiber is coarse and abrasive and is not suitable for delicate critical image surfaces, such as the photoconductor.
In order to provide a more conformable and less abrasive cleaning material, thermoplastic fibers were mixed with the aramid fibers in the nonwoven, such as is Japanese Laid Open Patent Application (Kokai) No. 5-119688, to Teijin Ltd. This publication discloses that the mix of fibers provides a less abrasive and better cleaning surface. While the thermoplastic fibers are less abrasive, use of these materials is severely limited by the temperature limitations of thermoplastic fibers. Typically, polyester fiber is the thermoplastic fiber of choice which will melt and become weak at fusing temperatures of 180.degree. to 220.degree. C. If the polyester is left on the fuser for too long, it can become fused to the fuser roller and cause system failures.
Another approach is to use a mixture of higher temperature fibers as described in Japan Laid Open Patent Application (Kokai) No. 4-83283 to Japan Vilene Co., Ltd. In this application, a mixture of aromatic polyamide fibers and undrawn polyphenylene sulfide (PPS) fibers are blended together in a nonwoven cleaning web. The fibers are thermally compressed under a temperature at which the undrawn PPS fibers are plasticized and act to fuse the fibers together. This mixture of fibers is capable of higher thermal stability and can be used in high speed printing applications where the fusing temperatures are raised. Because the printing speed is increased, the paper is not in contact with the fuser roller for as long a period of time. Therefore, the temperature of the fuser must be increased in order to provide sufficient heat energy to properly fuse the image. The fibers used in this application typically have a denier of 1 to 20.
Another approach, as described in Japanese Laid -Open (Kokai) No. 2-115883 to Canon Inc., is to use fluororesin fibers in the nonwoven web. The fluororesin material is less abrasive and has the high temperature capabilities needed for fusing temperatures. The amount of fluoropolymer fiber used in the nonwoven is, however, limited due to strength. If more than 80% fluororesin fiber is used, the mechanical properties are not acceptable for the cleaning web application.
Yet another approach described in U.S. Pat. No. 4,862,221 to Minolta Camera Kabushiki Kaisha, comprises a cleaning web with a concave-convex pattern. The purpose of the pattern is to improve the cleaning and contaminate holding capabilities of the web. In addition, U.S. Pat. No. 4,686,132 to Japan Vilene Co., Ltd., comprises a nonwoven cleaning web of aramid and polyester fiber having sealed portions and non-sealed portions. Again, the purpose of the sealed portions is to improve the cleaning performance of the web.
These publications are representative of cleaning webs which have been adapted to meet a variety of needs. However, to date, the art has been unable to provide an apparatus for cleaning the critical imaging surfaces in non-impact printing devices which is conformable, non-abrasive, thermally stable, microporous, and durable.
Accordingly, it is a primary purpose of the present invention to provide an apparatus for cleaning the critical imaging surfaces in non-impact printing devices which is conformable, non-abrasive, thermally stable, microporous, and durable. Moreover, further purposes of the present invention include:
(1) providing a cleaning apparatus material that utilizes microporous PTFE as the contaminate holding reservoir that is indexed by the critical imaging surface; PA0 (2) providing a thin cleaning apparatus material that reduces the space taken up by the apparatus; PA0 (3) providing a cleaning apparatus material that is substantially more conformable to contaminate scratches, and defects in or on the critical image surface than conventional materials; PA0 (4) providing a cleaning apparatus material that is less abrasive than conventional nonwovens; PA0 (5) providing a cleaning apparatus material that is strong; PA0 (6) providing a cleaning apparatus material that has low frictional characteristics; PA0 (7) providing a cleaning apparatus material that can easily incorporate fillers to alter the properties of the apparatus; PA0 (8) providing a cleaning apparatus material that can be thermally embossed in order to improve the contamination holding capacity; PA0 (9) providing a cleaning apparatus material with a high consistency in thickness and density; PA0 (10) providing a cleaning apparatus material that can present a 100% fluoropolymer surface to the critical imaging surfaces; and PA0 (11) providing a cleaning apparatus that can continually coat a critical imaging surface with a fluoropolymer release layer.
These and other purposes of the present invention will become evident based upon a review of the following specification.